Field of the Invention
The present invention relates to image processing to remove components, such as fog, in an image.
Description of the Related Art
In the field of the surveillance camera etc., there is such a problem that visibility is reduced due to fine particles (e.g., fog) existing between the camera and a subject and the quality of a captured image deteriorates. The techniques to remove the components, such as fog, have been proposed in Japanese Patent Laid-Open No. 2012-221237 and in “Single Image Haze Removal Using Dark Channel Prior”, CVPR 2009 by K. He, J. Sun and X. Tang. In these techniques, fog etc. is removed by calculating the transmittance with respect to fog etc. of light that reaches each pixel based the smallest pixel value of the pixel values of RGB channels of each pixel and by correcting the pixel value of each pixel in accordance with the transmittance.
However, in the above-described techniques, there may be a case where the white balance is disturbed in the image after components, such as fog, are removed. This results from the removal of only components, such as fog, from the image in the state where the white balance is adjusted in accordance with the sum total of the color of the subject and that of the fog etc.
In the case where components, such as fog, are removed, the pixel value is corrected so that the width of the gradation narrowed by the influence of fog etc. is extended, and therefore, noise is also amplified at the same time. The amount of amplification of noise differs depending on the position in the captured image (difference in transmittance from pixel to pixel), and therefore, even in the case where noise reduction processing is performed uniformly on the whole of the captured image, there appear portions where noise reduction is insufficient and portions where noise reduction is excessive depending on the position in the captured image.